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Digital Image Processing 2
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Research on the geometric model of the aeroscanning images
- Model analysing
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Aided data can be acquired by the method of pyramid
Fig.1 is the curve of the orientation elements changing with time T, using ten aerial images which are synchronous with scannor, these elements are calculated by the method of pyramid. 'o' indicate the positions of the projectional center of scanning lines which the ground points are in. after binated the six curvese, we can that the deformations of images are coplicated. And the course deformations are small. The average of linear element yo is used as the reducing calculation direction the reducing value Yo of projectional center for every scanning line is calculated. The reduced pixel I' is calculated by Yo' and another five orientation elements and geographic coordinates, with formula (5), the relation between the reducing value (I',L) of image coordinates and ground coordinates is set up.
Eq.5
With formula(5), the parameters c and d are calculated by least squares method. The I' and L in formula (5) are image coordinates after the longitude coordinates after the longitude correction (formula (2) and reducing correction.
The difference DI of I and I' can be interpolated with cubic parameter splines according to formula (3), (4) the corrected value Din of reducing image I for each scanning line is calculated, the corresponding relation between I+Din (this is In') and ground coordinates can be realized with parameter, c and d in formula (5).
Fig. 1
- Geometric model using ground linear feature
In general, plain and developed regions, the ground linear features are rich, such as highway, artificial canal, country road. Using de formations of linear features in scanning image and secreting the deformated characteristic pints to acquire the image coordinate (I, L).
With formula (3), (4), a number of characteristic points in A'B
(fig. 2) are selected, which can describe the image deformation, the number of pixels for each scanning line can be interpolated out by cubic parameter splines. The difference with A'B is used as the correction value. Selecting several sections of deformated image which are linear features in a view image, these sections are connected to each other and cover all scene.
We and geographic coordinates (x,y) and (I', L) of the corrected ground control points to calculate the parameters c and d by least squares method. This correction is mainly corrected the deformation in scanning direction, the deformation in course direction is less than that in scanning direction. The rest deformations can be corrected by completed bicubic multinomial. This also is a feasible method.
Fig. 2
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